1. Field of the Invention
The present invention relates to a shield for a hypodermic syringe assembly. More particularly, the present invention relates to a shield which can be retrofitted over an existing sheath/needle cannula sub-assembly of a hypodermic syringe assembly. Even more particularly, the present invention relates to a rigid shield which can be retrofitted over a resilient sheath which is being used to seal the distal end of a needle cannula of a prefilled hypodermic syringe prior to its use, the shield functioning to prevent needle sticks due to accidental piercing of the resilient sheath by the needle cannula.
2. Description of the Prior Art
It is common practice in the preparation of medications for use by medical workers, to pre-packaging the medications directly within a sealed hypodermic syringe assembly when such is a necessary vehicle for administration of the medication to a patient. According to this practice, a hypodermic syringe is sterilized and then prefilled with a predetermined amount of medication in a sterile environment, and the medication is sealed into the syringe by sealing the distal end of the needle cannula. The syringe is then packaged singly or in a predetermined quantity, into packaging which can be sterilized to maintain the sterility of the syringes until the medication is to be administered to a patient. In following this procedure, it has often been the practice to seal the distal end of the needle cannula with a resilient needle sheath. A sheath of this type is usually formed of a resilient rubber material with an elongate cavity therein which can accept the needle cannula. Generally, the sheath is formed so as to be capable of forming a friction fit with the hub of the needle cannula to hold the sheath in position over the needle. The cavity is sized so as to either fit snugly around the distal tip of the needle cannula, or to allow the distal tip of the needle cannula to pierce the distal end of the sheath and become embedded therein. In either case, the sheath effectively seals the tip of the needle cannula to prevent fluid from flowing therethrough out of the syringe during storage or prior to use.
Although the resilient needle sheath is generally quite successful in sealing the needle cannula, there remains serious concerns in the use thereof. Specifically, due to the piercability of the sheath, there exists a possibility of medical workers accidentally receiving a needle stick while using the syringe. This usually occurs either during preparation of the syringe for administration of medication to a patient, or during disposal procedures therefor. For example, since the sheath is formed of a resilient rubber, a minimal force improperly applied is all that is needed to cause the needle tip to penetrate (and even pierce entirely through) the sheath. Therefore, inadvertent pressure on the tip of the sheath during handling of the syringe assembly, may cause the needle to pierce entirely through the sheath's distal end and become exposed.
Further, medical workers often attempt to reinsert the needle into the sheath after the syringe has been used and prior to its disposal, even though this procedure is generally not recommended. Misalignment of the needle with the sheath during reinsertion can cause the tip of the needle to pierce through the side of the sheath where it may contact the hand of the medical worker holding it. Needle protrusion of this nature can readily occur since the tip of commonly used needles is ground off-center (i.e. on a bias) and therefore proceeds in a non-linear path when piercing the resilient sheath material. The needle tends to follow the off centered point as it passes through the sheath and in effect "skives off" in an arcing path of travel as it passes through the sheath material. If a medical worker is not extremely careful to let the needle center itself in the sheath cavity during reinsertion, the needle may inadvertently contact the side of the sheath cavity and pierce through the sheath material in a surprisingly unexpected direction, catching the medical worker off guard and likely causing a stick to the hand of the medical worker holding the sheath.
Although rigid, substantially impenetrable shields are commonly used to cover needle cannulas of hypodermic syringe assemblies, they are generally unsuitable for use on syringes which have been prefilled with a fluid such as a liquid medicament, due to their inability to seal the end of the needle cannula from fluid flow therethrough during storage and prior to use.
There have been attempts in the past to develop a substantially impenetrable shield which can be positioned over a resilient sheath commonly used on prefilled syringes in order to provide added protection to a medical worker from accidental needle sticks. For example, U.S. Pat. No. 4,964,866 to Szwarc discloses a needle shield assembly for use on a prefilled syringe. The assembly includes a resilient sheath, generally of the above described prior art construction, permanently enclosed in a rigid shield. The entire needle shield assembly (including the resilient sheath permanently enclosed in the rigid shield) is positioned over the needle cannula and thus seals the lumen of the needle cannula while simultaneously aiding in the prevention of needle sticks due to an accidental protrusion of the needle through the sheath.
Although this invention is a substantial improvement over the use of a resilient sheath alone in preventing accidental needle sticks, it is nevertheless somewhat limited in its use, and generally unadaptable to the myriad of different structural designs of commonly used prefilled hypodermic syringe assemblies. Specifically, the Szwarc needle shield assembly cannot be conveniently used to "retrofit" previously filled, sheathed, and sterilized prefilled hypodermic syringe assemblies.
Also, the design of the Szwarc device prevents its use as a retrofittable sub-assembly over a previously sheathed hypodermic syringe. This is because the Szwarc shield is manufactured in such a way as to require its assembly about the sheath prior to the sheath's placement over the needle cannula. This prevents any use of Szwarc over a previously sheathed and sterilized needle cannula. Prematurely removing the sterilized sheath of a needle/sheath assembly would be required in order to replace it with the encapsulated sheath of the Szwarc shield/shield.
An attempt to use the Szwarc device in such a retrofit manner would necessitate the removal of the original resilient sheath which was placed over the needle cannula prior to its sterilization, and subsequent insertion thereover of Szwarc's sheath/needle sub-assembly. Such a procedure would likely not be recommended due to the possibility of contamination of the needle cannula during the retrofitting process.
Also since it is important for a sheath to be properly sized in order to seal a needle cannula, the Szwarc device, in order to properly function to seal a needle cannula, must generally be manufactured to dimensions required by a particular syringe assembly design. Therefore, other needle cannula's (and sheath's therefor) of a substantially different size (e.g. shorter or longer in length) than specifically anticipated by Scwarc's design, cannot be used therewith.
There exists therefore a need to develop a shield which can be retrofitted over a sheath of a prefilled hypodermic syringe assembly by a medical worker, after the sheath has been positioned and sterilized, and prior to using the assembly. Further, it is necessary that such retrofitting procedure not compromise the sterility of the needle prior to its use nor require a premature removal of the sheath in order to install the shield.
There also exists a need in the prior art to develop a needle shield which can be used on various sizes and lengths of needle cannula and sheaths therefor.
Staebler, in U.S. Pat. No. 4,742,910, teaches another needle sheath holder which consists of a hollow barrel member adapted to be held in the hand of a medical worker. Staebler also includes a protective plate mounted to an open end of the barrel through which a sheath/needle sub-assembly of a hypodermic syringe assembly can be inserted. The plate is designed to protect the medical worker's hand during the insertion process. Finally, the Staebler device further includes a plurality of flexible gripper members attached at the barrel opening which are intended to engage the needle sheath so as to retain the needle sheath within the barrel.
Although the Staebler device seems an improvement over the Szwarc device in its retrofit capabilities, it nevertheless suffers from several drawbacks. Most notably, the Staebler device includes three separate parts (i.e., the barrel, the plate, and the gripper members) which must be individually manufactured and subsequently assembled, resulting in relatively expensive manufacturing costs. Further, it is not readily evident from the Staebler disclosure that a sheath formed of resilient material, such as resilient rubber (as opposed to what seems to be shown by Staebler as a relatively rigid sheath) could be successfully inserted into and retained by Staebler's barrel shield.
There therefore exists a need in the prior to develop a retrofittable shield for use over a resilient sheath of a hypodermic syringe assembly which is simple in design and inexpensive to manufacture.
In U.S Pat. No. 4,636,201, Ambrose et al. teaches the placement of a rigid shield over a rubber sheath of a hypodermic syringe. The rigid shield includes a plurality of spaced teeth members which are located at (and essentially form) the opening of the shield through which the sheath/needle sub-assembly of the syringe assembly is to be inserted. At least a pair of the teeth of the shield include a lip which projects inwardly toward the center of the opening to close in over the proximal end of the sheath once completely inserted into the shield.
Although Ambrose et al. allows a retrofit procedure to be performed on a hypodermic syringe assembly in a manner similar to Staebler, and also anticipates use of its device over a resilient sheath, there are nevertheless several important drawbacks of the Ambrose et al. device. Specifically, due to the location of the teeth on the Ambrose et al. device, it is difficult to ensure that a proper grip of the teeth about the proximal end of the sheath will occur. Many prior art sheath designs call for insertion of the sheath over the syringe needle hub until the proximal end of the sheath abuts a shoulder of the hub (generally at a location where the hub changes from a larger to a smaller diameter). This is a common design characteristic of a syringe hub and is useful to insure sealing of the sheath thereover. It also gives medical workers a visual and tactile indication that the sheath is properly positioned on the hub.
In such designs, there is no room for the teeth of the Ambrose et al. device to slip between the hub shoulder and the proximal end of a properly placed sheath in order to grip and retain the sheath in the manner Ambrose discloses. Due to this fact, use of the Ambrose et al. device on many common needle hub and sheath designs will not allow the teeth of the shield to properly attach themselves about the proximal end of the sheath. Only a syringe having a sheath/needle design which does not include abutment of the proximal end of the sheath against a shoulder of the needle hub will function properly with the Ambrose et al. device. Such a design limitation substantially inhibits the use of the Ambrose et al. device for purposes of retrofitting various common prefilled hypodermic syringe assemblies.
Further, medical workers may be hesitant to employ the Ambrose et al. device for retrofitting over sheaths of hypodermic syringe assemblies if they feel the shield may be less than completely reliable in gripping and retaining the sheath (e.g., due to the difficulties it may encounter if used on syringe assemblies having a hub design which differs from that shown in the Ambrose et al. disclosure).
Although it may seem at first glance that this problem may be avoided by initially partially removing the sheath from the needle hub prior to inserting the sheath into the Ambrose et al. shield (in order to space the proximal end of the sheath from the hub shoulder) such a procedure would likely be very unpopular with medical workers due to the inconvenience thereof. Such would also likely fail to resolve the problem since during insertion, the teeth of the Ambrose et al. needle shield contact and are forced apart by the sheath as the shield is positioned thereover. The teeth therefore force the sheath in the direction of the needle hub during placement of the shield. Subsequently, any attempt to separate the proximal end of the sheath from a shoulder of the needle hub prior to insertion of the sheath would be opposed by the force of the shield teeth on the sheath. The insertion force would likely reposition the proximal end of the sheath into abutting relationship with the shoulder of the needle hub prior to complete insertion of the sheath into the shield. The result would again be that the teeth would not be able to properly and securely grip the proximal end surface of the sheath.
There therefore exists a need in the prior art to develop a shield which can be retrofitted over an existing sheath of a prefilled hypodermic needle assembly and retain the sheath in the shield during subsequent removal and/or insertion of the needle into the sheath, without regard to the particular design of the sheath/needle hub connection.
Although the above prior art discloses a plurality of rigid shields used to protect medical workers against needle sticks from hypodermic syringes having resilient sheaths, there nevertheless continues to be a need for a rigid, substantially impermeable needle shield which can be simply and easily retrofitted over a range of sizes and designs of prefilled hypodermic syringes, without compromising the sterility of the needle cannula and with substantial reliability of retention of the sheath in the shield. Further, such a needle shield is needed which can also be manufactured as a single integral unit requiring no assembly of individual parts, so as to be simple to manufacture and relatively inexpensive.